Texas City, TX Environmental Rules: Flood Elevation Requirements (2026)

Section 157.41 sets the specific elevation standards wherever base flood elevation data has been provided. For residential structures, new construction and substantial improvement must have the lowest floor, including basement, elevated to or above the base flood elevation, and a registered professional engineer, architect or land surveyor submits a certification to the Floodplain Administrator that the standard is met. Substantial improvement means repair, reconstruction or improvement costing 50% or more of the structure's market value, measured under § 157.05.\n\nCommercial, industrial and other non-residential buildings have two routes.

They can elevate the lowest floor to or above the base flood level, or they can be floodproofed so the structure, with its utility and sanitary facilities, is water-tight below the base flood level with walls substantially impermeable to water. An engineer or architect must certify the floodproofed design, and the Floodplain Administrator keeps a record of the specific elevation to which the structure is floodproofed.\n\nFully enclosed areas below the lowest floor must equalize flood forces automatically. The minimum criteria in § 157.41(C) call for at least two openings with a total net area of not less than one square inch for every square foot of enclosed area, and the bottom of every opening no higher than one foot above grade.

Manufactured homes in Zones A1-30, AH and AE must sit on a permanent foundation with the lowest floor at or above the base flood elevation.\n\nThe city also reaches outside the mapped zones. Under § 157.40(H), new construction or substantial improvement in a non-special flood hazard area must be built at seven feet mean sea level or 18 inches above the curb of the street, whichever is greater. In shallow flooding AO and AH zones, § 157.43 requires the lowest floor at least as high above the highest adjacent grade as the depth number on the FIRM, and at least two feet if no depth number is specified.